Properties of Biodiesel and Other Biogen ic F ue ls Gerhard Knothe USDA / ARS / NCAUR Peoria, IL 61604 U.S.A. E-mail: [email protected] 1 Background • Energy security • Reduce dependence on petroleum-derived fuels • Derived from renewable resources • Enhance domestic (agricultural) economy • “GreenGreen” benefits: Biodegradability, reduced exhaust emissions 2 Historical Background Biofuels are not a recent concept. • Considerable research and use in the early 1900’s. • “Age of petroleum” approximately from 1945 to the 1970’s. • Renewed interest in alternative fuels in the 1970’s due to energy crises. 3 Historical Background • Vegetable oil-based fuels • First demonstration at the 1900 World Exposition • Interest through the early 1940’s • Late 1940’s / early 1950’s some work at Ohio State U and Georgia Institute of Technology • First biodiesel described in 1937 Belgian Patent 422,877 • Ethanol • Use and interest as blends / antiknock agent with gasoline through the 1930’s. • Tetraethyl lead as antiknock agent discovered in 1920’s 4 Petroleum-Based Fuels Hydrocarbons: • Gasoline: “Lighter” branched hydrocarbons • Exemppylified by 2,2,4-trimethyyplpentane ( iso-octane) • Diesel fuel: Long straight-chain hydrocarbons • Exemplified by hexadecane (cetane) • Jet fuel: “Light” diesel fuel 5 Biogenic Fuels / Biofuels • Most common biogeni c f uel s are oxygenated : • Alcohols (ethanol, butanol): By fermentation of carbohydrates • Gasoline replacement • Fatty acid methyl (alkyl) esters: By transesterification of triacylglycerol-containing materials • Diesel fuel replacement • Other biofuels include DME, biomethanol, biohydtrogen • More recently, hydrocarbon fuels from biofeedstocks (renewable diesel, biogasoline) simulating petrofuels developed 6 Biodiesel and Renewable Diesel Biodiesel Renewable Diesel Methyl (alkyl) esters Hydrocarbons By transesterification By hydrodeoxygenation Positive energy balance Energy balance? No/ low sulfur and aromatics Regulated exhaust emissions reduced compared to conventional petrodiesel Exception: NOx Cold flow problematic Cold flow varies /”adjustable” “Lighter” form”: aviation fuel Oxidative stability problematic High oxidative stability High lubricity Low lubricity Biodegradable Biodegradability likely similar to conventional petrodiesel Higher flash point Flash point likely closer to petrodiesel Feedstock availability and costs problematic Well-researched Other issues? 7 Fuel Suitability of Fatty Acid Methyl (Alkyl) Esters • Long-chain, unbranched alkanes are “ideal” petrodiesel fuels. • At least in terms of combustion. • Branched compounds and aromatics have low CNs • Structural similarity of long-chain, unbranched alkanes shows suitability of fatty esters as diesel fuels. • Long-chain fatty compounds such as methyl palmitate and methyl stearate have CN comparable to hexadecane • Minimum CN in biodiesel standards > than in petrodiesel standards. • 47 in ASTM D6751 (biodiesel) vs. 40 in ASTM D975 (petrodiesel). • 51 in EN 14214 (biodiesel) vs. 51 in EN 590 (petrodiesel) 8 Why biodiesel and not the neat oil? 1 1 OOCR CH2OH׳CH2-OOCR R | Catalyst | OOCR2 + CHOH׳OH → R׳CH-OOCR2 + 3 R || 3 3 OOCR CH2OH׳CH2-OOCR R Vegetable Oil Alcohol Vegetable Oil Alkyl Esters Glycerol (Triacylglycerol) (Biodiesel) Viscosity! 27-35 mm2/sec 4-5 mm2/sec Kinematic viscosity of petrodiesel fuels usually ≈ 1.8-3.0 mm2/sec. 9 Biodiesel and Alcohols • Biodiesel • Properties can vary considerably depending on the feedstock • Feedstocks can have widely varying fatty acid profiles • “Conventional” oils, i.e. classical commodity oils and many “alternative” oils contain mainlyyp palmitic, stearic, oleic, linoleic and linolenic acids. • Other oils may contain shorter or longer chain acids • Many algal oils contain highly polyunsaturated fatty acids. • Alcohol fuels • Same product independent of the feedstock 10 Some Fuel and Physical Properties of Ethanol and Butanol Ethanol Butanol Octane number (RON/MON*) 107-112 / 88-90 92-96 / 71-79 Meltinggp point ( °C) -114 -88.6 Boiling point (°C) 78.3 117.7 Heating value [MJ/kg], [MJ/l] 29, 23 37, 30 * RON = research octane number, MON = motor octane number • Suitability of alcohols as fuel (component) demonstrated by high octane number similar to cetane number of biodiesel. 11 Biodiesel Standard ASTM D6751 Property Test method Limits Units Flash point (closed cup) D 93 93 min oC Alcohol control . One of the following must be met: 1. Methanol content EN 14110 0.2 max % volume 2. Flash point D 93 130 min 130 min Water and sediment D 2709 0.050 max % volume Kinematic viscosity, 40 oC D 445 1.9-6.0 mm2 / s Sulfated ash D 874 0.020 max % mass Sulfur D5453 0.05 or 0.0015 max a) % mass Copper strip corrosion D 130 No. 3 max Cetane number D 613 47 min Cloud point D 2500 Report oC Carbon residue D 4530 0.050 max % mass Acid number D 664 0.50 max mg KOH / g Free glycerin D 6584 0.020 % mass Total glycerin D 6584 0.240 % mass Phosphorus content D 4951 0.001 max % mass Distillation temperature, D 1160 360 max oC Atmospheric equivalent temperature, 90% recovered Sodium and potassium, combined EN 14538 5 max ppm (μg/g) Calcium and magnesium, comb. EN 14538 5 max ppm (μg/g) Oxidation stability EN 15751 3 min hours Cold soak filterability D7501 360 max sec a) The limits are for Grade S15 and Grade S500 biodiesel, respectively. S15 and S500 refer to maximum sulfur specifications (ppm). 12 Biodiesel Standard EN 14214 Property Test method Limits Units Ester content EN 14103 96.5 min % (m/m) Density; 15oC EN ISO 3675, 12185 860-900 kg/m3 Viscosity, 40 oC EN ISO 3104 , ISO 3105 353.5-505.0 mm2/s Flash point EN ISO 2719, 3679 101 min oC Sulfur content EN ISO 20846, 20884 10.0 max mg/kg Carbon residue (10% dist. res.) EN ISO 10370 0.30 max % (m/m) Cetane number EN ISO 5165 51 min Sulfated ash ISO 3987 0.02 max % (m/m) Water content EN ISO 12937 500 max mg/kg Total contamination EN 12662 24 max mg/kg Copper strip corrosion (3h , 50 oC) EN ISO 2160 1 Oxidative stability, 110 oC EN 14112, 15751 8.0 min h Acid value EN 14104 0.50 max mg KOH / g Iodine value EN 14111 120 max g iodine /100g Linolenic acid content EN 14103 12 max %(m/m) Content of FAME with ≥ 4 double bonds 1 max % (m/m) Methanol content EN 14110 0.20 max % (m/m) Monoglyceride content EN 14105 0.80 max % (m/m) Diglyceride content EN 14105 0200.20 max % (m/m) Triglyceride content EN 14105 0.20 max %(m/m) Free glycerine EN 14105, 14106 0.02 max %(m/m) Total glycerine EN 14105 0.25max %(m/m) Alkali metals (Na + K) EN 14108, 14109, 14538 5.0 max mg/kg Earth alkali metals (Ca + Mg) prEN 14538 5.0 max mg/kg Phosphorus content EN 14107 4.0 max mg/kg 13 Major Ester Components of Most Biodiesel Fuels Fatty esters in from common vegetable oils (palm, soybean, canola/rapeseed, sunflower, etc): • Methyl palmitate (C16:0): CH3OOC-(CH2)14-CH3 • Methyl stearate (C18:0): CH3OOC-(CH2)16-CH3 • Methyy(l oleate (C18:1, Δ9c): CH3OOC-(CH2)7-CH=CH-(CH2)7-CH3 • Methyl linoleate (C18:2; all cis): CH3OOC-(CH2)7-(CH=CH-CH2)2-(CH2)3-CH3 • Methyl linolenate (C18:3; all cis): CH3OOC-(CH2)7-(CH=CH-CH2-)3-CH3 From other oils: • Methyl laurate (C12:0): CH3OOC-(CH2)10-CH3 • Methyl ricinoleate (C18:1, 12-OH; cis): CH3OOC-(CH2)7-CH=CH-CH2-CHOH-(CH2)5-CH3 14 Properties of Methyl Esters Cetane M.P. Kin. Visc. Oxid. Heat of Number (°C) (40°C; mm2/s) Stab. (h) Comb. (kJ/kg) C12:0 67 4.5 2.43 > 24 37968 C16:0 85 28.5 4.38 > 24 39449 C18:0 100 38 5.85 > 24 40099 C18:1 58 -20 4.51 2.79 40092 C18:2 38 -43 3.65 0.94 39698 C18:3 23 -52 3.14 0 39342 C18:1 12-OH 37 -5 15.29 0.67 ASTM 6751 47 min CP 1.9-6.0 3 min - EN 14214 51 min CFPP 3.5-5.0 8 min - G. Knothe; Energy & Fuels 22, 1358-1364 (2008). 15 Some Fatty Acid Profiles Vegetable Oil C16:0 C18:0 C18:1 C18:2 C18:3 Rapeseed / Canola 3-4 1-3 58-62 20-22 9-12 Soy 8-13 2-6 18-30 49-57 2-10 Sunflower 6-7 3-5 21-29 58-67 Jatropha 13-15 7-8 34-44 31-43 16 Properties of Vegetable Oil Esters Methyl Ester Cloud Point Cetane Number Kin. Visc. (°C) (40°C; mm2/s) Rapeseed / Canola -3 52-55 4.5 Soy 0 48-52 4.1 Sunflower 0 ≈ 55 4.4 Jatropha 4-5 Oxidative stability: usually antioxidants required to meet standard specifications 17 Property Trade-off Increasing chain length: • Higher melting point (-) • Higher cetane number (()+) Increasing unsaturation: • Lower melting point (+) • Decreasing oxidative stability (-) • Lower cetane number (-) 18 Influence of Alcohol Moiety Branched and longer -chain esters: ● Lower melting points, similar cetane numbers compared to methyl esters Ester M.P. (°C) CN Ester M.P. (°C) CN C16:0 Methyl 28.5 85.9 C18:0 Me 37.7 101 C16:0 Ethyl 23.2 93.1 C18:0 Et 33.0 97.7 C16:0 Propyl 20.3 85.0 C18:0 Pr 28.1 90.0 C16:0 iso-Propyl 13-14 82.6 C18:0 i-Pr 96.5 C18:1 Methyl -20.2 59.3 C18:2 Me -43.1 38.2 C18:1 Ethyl -20.3 67.8 C18:2 Et -56.7 39.6 C18:1 Propyl -30.5 58.8 C18:2 Pr 44.0 C18:1 iso-Propyl 86.6 ● Disadvantage: Higher costs of alcohols Source: Handbook of Chemistry and Physics; The Lipid Handbook, various publications. 19 Five Approaches to Improving Biodiesel Fuel Properties Unchanged fatty Additives A ester composition Change B alcohol Physical procedures C Modified fatty ester composition Change fatty acid Genetic profile D modification Inherently different fatty acid profile Alternative E feedstocks G.